# Voltage Drop Compendium

Discussion in 'Landscape Lighting' started by INTEGRA Bespoke Lighting, Dec 11, 2007.

1. ### Lite4LawnSite Gold Memberfrom Indianapolis, INMessages: 3,170

You know I have always wondered about different manufacturers wire as well. Testing the same length and guage of wire of 3 or 4 different manufacturers and see if all the wire is fairly even.

2. ### klkandersLawnSite Senior Memberfrom MidwestMessages: 849

Can I just say I love saying the word "Compendium". I love reading these posts late at night, they are great, but they sometimes make me soporific.

3. ### INTEGRA Bespoke LightingLawnSite Platinum Memberfrom Muskoka, Ontario, CanadaMessages: 4,102

Reading never ending arguments can tend to make one soporific I find...

Ok so we have the Nightscaping Formula, and we have the Unique Formula, and we have the Vista Formula...

Are there any other, different Voltage Drop formulas out there that people know of? Not much of a compendium unless we find more then three....

Lets not break down into bickering about who does what to whom, where and when here... That doesnt enter into the scientific method as I recall. This isnt about exposing those who do VD analysis during planning or build out VS. those that use meters at the end of the job to balance Multi-Tap Transformers. This is simply to do some exploring and testing of method and accuracy.

4. ### INTEGRA Bespoke LightingLawnSite Platinum Memberfrom Muskoka, Ontario, CanadaMessages: 4,102

There has been some talk here that the Nightscaping Voltage Drop Formula is inaccurate and that it only applies to DC circuits. It has been suggested that when using this formula on AC circuits that the cable distance needs to be multiplied by two.

The people who suggest this state that the multiplication x 2 needs to be done because in an AC circuit the electricity must run the length of the wire and then back again.

As far as I understand it (that phrase is for you Pete), This is backwards thinking. In an AC circuit the electricity is "flowing" back and forth at 60hz, thus setting up a 'wave' of energy through the circuit. It is in a DC circuit that the electricity travels from one pole down the length of one side of the cable, through the load, and back down the other side of the cable to the other pole. (thuse twice the distance) This, as I understand it, (again for you Pete) is the inherent inefficiency of large or long DC circuits and thus one of the main reasons our electricity distribution system is an AC system

I stand to be corrected, but please, if I am wrong about this, take the time to fully and completely explain your rationale. Perhaps one of our electrical contractor friends might be able to chime in here. Could just set us all straight.

Thanks.

5. ### steveparrottSponsorfrom Tampa, FLMessages: 1,255

CAST uses the same formula as Unique - the most accurate that I know of.

The Nightscaping formula seems to be off because they don't have the 2X multiplier.

As far as calculators go, the system calculator on the CAST website is the most accurate and full-featured. It warns you when commons are overloaded and when wire ratings are exceeded. It also calculates energy cost.

6. ### JoeyDLawnSite Silver Memberfrom Escondido, CAMessages: 2,933

The CAST wire calculator is very nice I must admit!

I came by your booth (IA) Steve to say hello but you were not there. Just wanted to put a face to the name.

Maybe next time!!

7. ### steveparrottSponsorfrom Tampa, FLMessages: 1,255

Thanks Joey, sorry I missed you!

8. ### johnhLawnSite Memberfrom Toronto, ONMessages: 34

AC Circuits

For AC circuits, where AC resistance and inductive reactance are considered, the following is the IEEE Std 141 exact voltage drop formula.

where:
Vd = Voltage drop (Line to Neutral)
V = Voltage (source)
I = Current in amperes (A)
R = AC Resistance from NEC® Chapter 9 Table 9 (Ohms to Neutral)
X = AC Reactance from NEC® Chapter 9 Table 9 (Ohms to Neutral)
distance (L) is considered from the Resistance & Reactance Tables
where Ohms per unit / 1000 * L in same unit = R or X
&#952; = Angle of Phase Offset = Arc Cosine (device or circuit Power Factor)
Line to Line is computed by Line to Neutral VD / Sqrt(3).

DC Circuits

where:
Vd = Voltage drop
R = DC Resistance from NEC® Chapter 9 Table 8
L = Distance
I = Current in amperes (A)

K = Material Resistivity constant - 12.9 for Cu & 21.2 for Al
CM = Circular mils of conductor

These are the IEEE formulae if you've got a good calculator and a dictionary!
JH

9. ### INTEGRA Bespoke LightingLawnSite Platinum Memberfrom Muskoka, Ontario, CanadaMessages: 4,102

Oh gee thanks John! Now I have to ge get my electrical engineering degree to decipher all of that.

I dont suppose you would like to work that out into a working formula and then put it through a test for us would you?

10. ### Chris JLawnSite Silver Memberfrom Maldive IslandsMessages: 2,843

Stop it! I think I just pissed on myself!